Re: [PATCH 0/4] Swapping

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Izik Eidus wrote:
> Anthony Liguori wrote:
>   
>> Izik Eidus wrote:
>>     
>>> Anthony Liguori wrote:
>>>       
>>>> I've been playing around with these patches.  If I do an 
>>>> madvise(MADV_DONTNEED) in userspace, when I close the VM, I get the 
>>>> following bug.  My knowledge of the mm is limited but since 
>>>> madvise(MADV_DONTNEED) effectively does a zap_page_range() I wonder 
>>>> if we're lacking the necessary callback to also remove any potential 
>>>> GPA covered by that range from shadow page cache.
>>>>
>>>> Regards,
>>>>
>>>> Anthony Liguori
>>>>         
>>> it probably beacuse the changes of the first patch, ( that make all 
>>> present shadow pages rmapped )
>>> Anthony can you please check what happn if you run latest kvm with 
>>> the patch (of the rmap) and without the patch?
>>>       
>> It looks like it's my patch for doing an in kernel mmap() to support 
>> older userspaces.  I'll figure out what the problem is.
>>
>> But at any rate, would madvise() be able to evict the current contents 
>> of something in the shadow page cache or will the guest not pick up 
>> the new memory until the old gets evicted from the shadow page cache?
>>     
> if i understand you right, then madvise() wont harm us, beacuse we 
> protect all our shadow memory by removing the writable bit from it.
> therefor the guest cant change anything without we know it.
>   

The host userspace can, though, and we need to protect the kernel from that.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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